Sulfur-impregnated activated carbon fiber cloth as a binder-free cathode for rechargeable Li-S batteries

Investigating PEDOT:PSS Binder as an Energy Extender in Sulfur Cathodes for Li-S Batteries

Although lithium-sulfur (Li-S) batteries offer a high theoretical energy density, shuttling of dissolved sulfur and polysulfides is a major factor limiting the specific capacity, energy density, and cyclability of Li-S batteries with a liquid electrolyte. Cathode host materials with a microstructure to restrict the migration of active material may not totally eliminate the shuttling effect or may create additional problems that limit the full dissolution and redox conversion of all active cathode materials. Selecting a cathode coating binder with a multifunctional role offers a universal solution suitable for various cathode hosts. PEDOT:PSS is investigated as such a binder in this study via experimental testing and material characterization as well as multiscale modeling. The study is based on Li-S cells with a sulfur cathode in hollow porous particles as the cathode host and the 10 wt % PEDOT:PSS binder and electrolyte 1 M LiTFSI in 1:1 DOL:DME 1:1 v/v. A reference supercapacitor cell with the same electrolyte and electrodes comprising a coating of the same hollow porous particles and 10 wt % PEDOT:PSS revealed the pseudocapacitive effect of PEDOT:PSS following a surface redox mechanism that dominates the charge phase, which is equivalent to the discharge phase of the Li-S battery cell. A multipore continuum model for supercapacitors and Li-S cells is extended to incorporate the pseudocapacitive effects of PEDOT:PSS with the Li+ ions and the adsorption effects of PEDOT:PSS with respect to sulfur and lithium sulfides in Li-S cells, with the adsorption energies determined via molecular and ab initio simulations in this study. Experimental data and predictions of multiscale simulations concluded a 7-9% extension of the specific capacity of Li-S battery cells due to the surface redox effect of PEDOT:PSS and elimination of lithium sulfides from the anode by slowing down their migration and shuttling via their adsorption by the PEDOT:PSS binder.

A Freestanding, Dissolution- and Diffusion-Limiting, Flexible Sulfur Electrode Enables High Specific Capacity at High Mass Loading

The acquisition of stable and high-areal-capacity S cathodes over 10 mA h cm-2 is a critical and indispensable step to realize the high energy density configuration. However, increasing the areal capacity of S cathodes often deteriorates the specific capacity and stability due to the aggravated dissolution of S and diffusion of solvable polysulfides in the thick electrode. Herein, the design of a freestanding composite cathode that leverages 3D covalent binding sites and chemical adsorption environment to offer dissolution-limiting and diffusion-blocking functions of S species is reported. By employing this architecture, the coin cell exhibits excellent cycling stability and an exceptional specific capacity of 1444.3 mA h g-1 (13 mA h cm-2), and the pouch cell configuration manifests a noteworthy areal capacity exceeding 11 mA h cm-2. This performance is coupled with excellent flexibility, demonstrated through consecutive bending cycle tests, even at a sulfur loading of 9.00 mg cm-2. This study lays the foundation for the development of flexible Li-S batteries with increased loading capacities and exceptional performance.

In Situ Electrochemical Restructuring B-Doped Metal-Organic Frameworks as Efficient OER Electrocatalysts for Stable Anion Exchange Membrane Water Electrolysis

Metal organic frameworks (MOFs) are promising as effective electrocatalysts toward oxygen evolution reaction (OER). However, the origin of OER activity for MOF-based electrocatalysts is still unclear because of their structure reconstruction during electrocatalysis process. Here, a novel MOF (B-MOF-Zn-Co) with spherical superstructure is developed by hydrothermal treatment of zeolitic imidazolate framework-Zn, Co (ZIF-Zn-Co) using boric acid. The resultant B-MOF-Zn-Co shows high OER activity with a low overpotential of 362 mV at 100 mA cm-2. Remarkably, B-MOF-Zn-Co displays excellent stability with only 3.6% voltage delay over 300 h at 100 mA cm-2 in alkaline electrolyte. Surprisingly, B-MOF-Zn-Co thoroughly transforms into B-doped CoOOH (B-CoOOH) during electrolysis process, which is served as actual active material for high OER electrocatalytic performance. The newly-formed B-CoOOH possesses lower energy barrier of potential-determining step (PDS) for OOH* formation compared with CoOOH, benefiting for high OER activity. More importantly, B-MOF-Zn-Co based anion exchange membrane water electrolytic cell (AEMWE) demonstrates continuously durable operation with stable current density of 200 mA cm-2 over 300 h, illustrating its potential application in practice water electrolysis. This work offers an in situ electrochemical reconstruction strategy for the development of stable and effective OER electrocatalysts toward practice AEMWE.

Multiscale Structural Design of 2D Nanomaterials-based Flexible Electrodes for Wearable Energy Storage Applications

2D nanomaterials play a critical role in realizing high-performance flexible electrodes for wearable energy storge devices, owing to their merits of large surface area, high conductivity and high strength. The electrode is a complex system and the performance is determined by multiple and interrelated factors including the intrinsic properties of materials and the structures at different scales from macroscale to atomic scale. Multiscale design strategies have been developed to engineer the structures to exploit full potential and mitigate drawbacks of 2D materials. Analyzing the design strategies and understanding the working mechanisms are essential to facilitate the integration and harvest the synergistic effects. This review summarizes the multiscale design strategies from macroscale down to micro/nano-scale structures and atomic-scale structures for developing 2D nanomaterials-based flexible electrodes. It starts with brief introduction of 2D nanomaterials, followed by analysis of structural design strategies at different scales focusing on the elucidation of structure-property relationship, and ends with the presentation of challenges and future prospects. This review highlights the importance of integrating multiscale design strategies. Finding from this review may deepen the understanding of electrode performance and provide valuable guidelines for designing 2D nanomaterials-based flexible electrodes.

Aqueous heterocoagulation-driven assembly of graphene oxide and polycation-coated sulfur particles for nanocomposite Li-S battery cathodes

HYPOTHESIS

Reduced graphene oxide (rGO/polycation/sulfur) composites are promising cathode materials for Li-S battery applications because homogeneously dispersed sulfur nano/micro clusters in suitable carbon hosts enable remarkable cycle life for Li-S battery cells. New, benign and economic synthesis methods based only on aqueous colloidal dispersions are demanded for achieving high dispersity grade of sulfur within the carbon host. Colloidal interactions leading to heteroaggregation between carbonaceous lamellae and polycation-modified sulphur nanoparticles at ambient conditions in water are foreseen to afford nanocomposite cathodes, which maintain excellent electrochemical performance.

EXPERIMENTS

Hydrophilic sulfur nanoparticles (SNPs) were coated by low doses of polycation (PDDA) until reaching the isoelectric point (IEP), and in high dose to achieve charge reversal. Streaming potential titrations were performed to reveal appropriate mass ratios of PPDA, SNP and GO. Positively charged SNPs formed stable heteroaggregated structures with GO, and were employed to fabricate rGO/polycation/sulphur cathodes.

FINDINGS

Charge reversal characteristics of SNPs, polycation and GO were characterized quantitatively and mass ratios of PDDA to SNP beyond IEP were found to mediate attractive interactions leading to rapid heteroaggregation between SNPs and GO and also alleviate lithium polysulfide migration. The composite cathode showed an initial discharge capacity of 522 mAhg-1 at 0.2C rate with an excellent capacity retention of 91.4 % and coulombic efficiency of 98.5% after 100 charge-discharge cycles.

Carbon Nanotube-encapsulated Chestnut Inner Shell O,N-doped Graded Porous Carbon as Stable and High-Sulfur Loading Electrode for Lithium-Sulfur Batteries

The shuttle effect of lithium-sulfur (Li-S) batteries and the poor conductivity of sulfur (S) and lithium polysulfide severely limit their practical applications. Currently, compounding carbon materials with S is one of the effective ways to solve this problem. Therefore, green, low-cost chestnut inner shell biochar (CISC) with graded porous structure was used as the S carrier in this experiment, and carbon nanotubes (CNTs) coating was employed as the S protective layer to improve the electrical conductivity and inhibit the shuttle effect. The results showed that the CISC prepared in this experiment had a relatively high specific surface area (1135.11 m2  g-1 ), and the S loading rate was as high as 65.72 %. The graded porous structure and high specific surface area of CISC can increase the loading rate of S and thus increase the battery capacity. Meanwhile, the naturally contained O and N elements can improve the chemisorption of S. The initial discharge capacity of the CISC@S/CNTs battery at 0.1 C is 967.3 mAh g-1 , and the capacity retention rate is 74.3 % after 500 cycles. The unique composite structure improves the battery's electrical conductivity, reduces the dissolution of polysulfides, and enhances the battery cycle stability.

Material Choice and Structure Design of Flexible Battery Electrode

With the development of flexible electronics, the demand for flexibility is gradually put forward for its energy supply device, i.e., battery, to fit complex curved surfaces with good fatigue resistance and safety. As an important component of flexible batteries, flexible electrodes play a key role in the energy density, power density, and mechanical flexibility of batteries. Their large-scale commercial applications depend on the fulfillment of the commercial requirements and the fabrication methods of electrode materials. In this paper, the deformable electrode materials and structural design for flexible batteries are summarized, with the purpose of flexibility. The advantages and disadvantages of the application of various flexible materials (carbon nanotubes, graphene, MXene, carbon fiber/carbon fiber cloth, and conducting polymers) and flexible structures (buckling structure, helical structure, and kirigami structure) in flexible battery electrodes are discussed. In addition, the application scenarios of flexible batteries and the main challenges and future development of flexible electrode fabrication are also discussed, providing general guidance for the research of high-performance flexible electrodes.

Carbon Coated Metal-Based Composite Electrode Materials for Lithium Sulfur Batteries: A Review

Lithium-sulfur battery is one of the most promising secondary battery systems due to their high energy density and low material cost. During the past decade, great progress has been achieved in promoting the performances of Li-S batteries by addressing the challenges at the laboratory-level model systems. With growing attention paid to the application of Li-S batteries, new challenges at practical cell scales emerge as the bottleneck. However, challenges remain for the commercialization of lithium-sulfur batteries. The current review mainly focused on metal-based catalysts decorated-carbon materials for enhanced lithium sulfur battery performance. Firstly, the synthesis methods of various carbon-sulfur composites are discussed, as well as the influence of different material structures on the electrochemical performance. Secondly, a variety of catalysts, including metal atoms, metal oxides, sulfides, phosphides, nitrides, and carbide-decorated carbon nanomaterials, are systematically introduced to determine how lithium can be enhanced by suppressing polysulfides and promoting redox conversion reactions. Also, analyzed the multi-step electrochemical reaction mechanism of the battery during the charging and discharging process, and provide a feasible path for the practical application of high energy density lithium-sulfur batteries.

A Novel Triple Crosslinking Strategy on Carbon Nanofiber Membranes as Flexible Electrodes for Lithium-Ion Batteries

In order to solve the problem of low electrical conductivity of carbon nanofiber membranes, a novel triple crosslinking strategy, including pre-rolling, solvent and chemical imidization crosslinking, was proposed to prepare carbon nanofiber membranes with a chemical crosslinking structure (CNMs-CC) derived from electrospinning polyimide nanofiber membranes. The physical-chemical characteristics of CNMs-CC as freestanding anodes for lithium-ion batteries were investigated in detail, along with carbon nanofiber membranes without a crosslinking structure (CNMs) and carbon nanofiber membranes with a physical crosslinking structure (CNMs-PC) as references. Further investigation demonstrates that CNMs-CC exhibits excellent rate performance and long cycle stability, compared with CNMs and CNMs-PC. At 50 mA g⁻¹, CNMs-CC delivers a reversible specific capacity of 495 mAh g⁻¹. In particular, the specific capacity of CNMs-CC is still as high as 290.87 mAh g⁻¹ and maintains 201.38 mAh g⁻¹ after 1000 cycles at a high current density of 1 A g⁻¹. The excellent electrochemical performance of the CNMs-CC is attributed to the unique crosslinking structure derived from the novel triple crosslinking strategy, which imparts fast electron transfer and ion diffusion kinetics, as well as a stable structure that withstands repeated impacts of ions during charging and discharging process. Therefore, CNMs-CC shows great potential to be the freestanding electrodes applied in the field of flexible lithium-ion batteries and supercapacitors owing to the optimized structure strategy and improved properties.

Facile Dissolution-Crystallization Strategy to Achieve Rapid and Uniform Distribution of Sulfur on Porous Carbon for Lithium-Sulfur Batteries

In this work, we proposed a facile dissolution-crystallization strategy based on density functional theory calculations to achieve rapid as well as uniform distribution of sulfur on porous carbon. Sulfur-containing solution can completely penetrate porous material and in preference remove into the pores under the influence of capillary force, and sulfur tends to crystallize on the defective even non-defective carbon matrix rather than agglomerate. The S/PC composites prepared by this method can still achieve uniform distribution of sulfur when the sulfur content is as high as 85%. All operations can be completed within a few minutes without any heating. Compared with common melt-diffusion and vapor-phase infusion, this approach has lower energy consumption and is simple, safe, continuous, and rapid.

Unveiling the Electrocatalytic Activity of 1T'-MoSe2 on Lithium-Polysulfide Conversion Reactions

The dissolution of intermediate lithium polysulfides (LiPS) into an electrolyte and their shuttling between the electrodes have been the primary bottlenecks for the commercialization of high-energy density lithium-sulfur (Li-S) batteries. While several two-dimensional (2D) materials have been deployed in recent years to mitigate these issues, their activity is strictly restricted to their edge-plane-based active sites. Herein, for the first time, we have explored a phase transformation phenomenon in a 2D material to enhance the number of active sites and electrocatalytic activity toward LiPS redox reactions. Detailed theoretical calculations demonstrate that phase transformation from the 2H to 1T' phase in a MoSe₂ material activates the basal planes that allow for LiPS adsorption. The corresponding transformation mechanism and LiPS adsorption capabilities of the as-formed 1T'-MoSe₂ were elucidated experimentally using microscopic and spectroscopic techniques. Further, the electrochemical evaluation of phase-transformed MoSe₂ revealed its strong electrocatalytic activity toward LiPS reduction and their oxidation reactions. The 1T'-MoSe₂-based cathode hosts for sulfur later provide a superior cycling performance of over 250 cycles with a capacity loss of only 0.15% per cycle along with an excellent Coulombic efficiency of 99.6%.

Multimodal Capturing of Polysulfides by Phosphorus-Doped Carbon Composites for Flexible High-Energy-Density Lithium-Sulfur Batteries

The widespread adoption of Li-ion batteries is currently limited by their unstable electrochemical performance and high flammability under mechanical deformation conditions and a relatively low energy density. Herein, high-energy-density lithium-sulfur (Li-S) batteries are developed for applications in next-generation flexible electronics and electric vehicles with long cruising distances. Freestanding high-S-loading carbon nanotubes cathodes are assembled with a phosphorus (P)-doped carbon interlayer coated on commercial separators. Strategies for the active materials and structural design of both the electrodes and separators are highly efficient for immobilizing the lithium polysulfides via multimodal capturing effects; they significantly improve the electrochemical performance in terms of the redox kinetics and cycling stability. The foldable Li-S cells show stable specific capacities of 850 mAh g^-1 over 100 cycles, achieving high gravimetric and volumetric energy densities of 387 Wh kg_cell ^-1 and 395 Wh L_cell ^-1 , respectively. The Li-S cells show highly durable mechanical flexibilities under severe deformation conditions without short circuit or failure. Finally, the Li-S battery is explored as a light-weight and flexible energy storage device aboard airplane drones to ensure at least fivefold longer flight times than traditional Li-ion batteries. Nanocarbon-based S cathodes and P-doped carbon interlayers offer a promising solution for commercializing rechargeable Li-S batteries.

In Situ Constructing a Stable Solid Electrolyte Interface by Multifunctional Electrolyte Additive to Stabilize Lithium Metal Anodes for Li-S Batteries

Lithium (Li) metal is considered to be the most promising anode due to the ultrahigh capacity and extremely low electrochemical potential. The tricky thing is that the growth of dendritic Li brings huge safety hazards to Li metal batteries. Herein, we demonstrate cerium nitrate as a multifunctional electrolyte additive to form a stable solid electrolyte interface on the metallic Li anode surface for durable Li-S batteries. The presence of Ce³⁺ helps to modulate the electroplating/stripping of Li and inhibits the growth of dendritic Li. An excellent cycle life exceeding 1400 h at the current density of 1 mA cm^-2 can be realized in symmetric Li||Li cells. In addition, the in situ formed robust solid-electrolyte interface (SEI) layer containing cerium sulfide on the Li anode surface conduces to weaken the reducibility of Li and regulate the electrochemical dissolution/deposition reaction on the Li anode. Surprisingly, by virtue of cerium nitrate additive with a low concentration of 0.03 M, the Li-S batteries can afford a capacity of 553 mA h g^-1 at 5 C and a long cycle life at 1 C with a high capacity retention of 70.4%. Therefore, this study provides a novel idea to realize a uniform and dendrite-free Li anode for practical Li-S batteries.

Tailoring Mesopores and Nitrogen Groups of Carbon Nanofibers for Polysulfide Entrapment in Lithium-Sulfur Batteries

In the current work, we combined different physical and chemical modifications of carbon nanofibers through the creation of micro-, meso-, and macro-pores as well as the incorporation of nitrogen groups in cyclic polyacrylonitrile (CPAN) using gas-assisted electrospinning and air-controlled electrospray processes. We incorporated them into electrode and interlayer in Li–Sulfur batteries. First, we controlled pore size and distributions in mesoporous carbon fibers (mpCNF) via adding polymethyl methacrylate as a sacrificial polymer to the polyacrylonitrile carbon precursor, followed by varying activation conditions. Secondly, nitrogen groups were introduced via cyclization of PAN on mesoporous carbon nanofibers (mpCPAN). We compared the synergistic effects of all these features in cathode substrate and interlayer on the performance Li–Sulfur batteries and used various characterization tools to understand them. Our results revealed that coating CPAN on both mesoporous carbon cathode and interlayer greatly enhanced the rate capability and capacity retention, leading to the capacity of 1000 mAh/g at 2 C and 1200 mAh/g at 0.5 C with the capability retention of 88% after 100 cycles. The presence of nitrogen groups and mesopores in both cathodes and interlayers resulted in more effective polysulfide confinement and also show more promise for higher loading systems.

Integration of porous graphitic carbon and carbon fiber framework for ultrahigh sulfur-loading lithium-sulfur battery

A lithium-sulfur battery, a potential next-generation secondary battery, is affected by poor conductivity of sulfur and the dissolution of intermediate polysulfides. Here we report a lithium-sulfur battery with ultrahigh sulfur loading and excellent cycling stability using porous graphitic carbon (PGC) as a high-conductivity carrier of sulfur and carbon fiber with crisscross conductive framework as an electric attachment site of sulfur. PGC is fabricated through a simple and environmentally friendly synthesis process involving high-temperature graphitization in a N₂ atmosphere followed by an annealing process in air. Due to the presence of porous graphitic structure, with C-O termination groups, PGC endows the lithium-sulfur battery system with excellent cycling performance. The lithium-sulfur battery cathode constructed by PGC with a sulfur loading of 2.5 mg cm^-2 still retains a high specific capacity of 734.4 mA h g^-1 after 200 cycles. Meanwhile, an ultrahigh sulfur loading of 12.8 mg cm^-2 for a CR2025 coin cell is achieved, which is the highest sulfur loading reported in the literature for the coin cell. The ultrahigh sulfur loading cell also shows good electrochemical properties, profiting from the mesopores terminated with C-O groups, high specific surface area of 1129.9 m² g^-1 and high-conductivity graphitic structure.

Cotton-Derived Fe/Fe3C-Encapsulated Carbon Nanotubes for High-Performance Lithium-Sulfur Batteries

Fabrication processes of fossil fuel-derived carbon nanomaterials are of high carbon emissions. Deriving carbon materials from low-cost and sustainable biomass is eco-friendly. Cotton, one of the most abundant biomass materials, naturally holds a hierarchically porous structure, making the activated cotton textile (ACT) an ideal scaffold for loading active materials. Here, we report a low-cost approach to massively producing multiwalled carbon nanotubes (MWCNTs) via a combination process of vapor-liquid-solid (VLS) and solid-liquid-solid (SLS) where cotton decomposed into carbon-containing gases and amorphous carbons that then dissolved into Fe nanoparticles, forming Fe/Fe₃C-encapsulated MWCNTs. The lithium-sulfur (Li-S) battery constructed by the Fe/Fe₃C-MWCNT@ACT/S composite (as the cathode) and the Fe/Fe₃C-MWCNT@ACT (as the interlayer) exhibited a superlative cycling stability (over 1000 cycles at 1.0 C), an ultralow capacity decay rate (0.0496% per cycle) and a remarkable specific capacity (1273 mAh g^-1 at 0.1 C). The Fe/Fe₃C-MWCNTs enhanced electrode stability and suppressed polysulfide dissolution during cycling.

A Comparative Study of Cobalt Chalcogenides as the Electrode Materials on Lithium-Sulfur Battery Performance

Lithium-sulfur batteries, as viable options for energy storage, have gained popularity because of their high energy density. However, the poor conductivity of sulfur and Li₂ S, as well as the shuttling effect of lithium polysulfides, seriously limits their commercialization. Herein, cobalt chalcogenides (Co₃ O₄ , CoS, and Co₃ Se₄ ) supported by reduced graphene oxide are synthesized as the electrode materials, which feature high conductivity, rapid kinetic conversion, and catalytic effect. Based on complementary experimental outputs and advanced computation, it is revealed that the change in anion results in distinctive performance. Among them, the cathode material based on Co₃ Se₄ /reduced graphene oxide is the best. The reasons can be ascribed to the conductive and catalytic improvement. This comparative study provides guidelines in the design of lithium-sulfur batteries via the meticulous regulation of the anions.

Carbonaceous Hosts for Sulfur Cathode in Alkali-Metal/S (Alkali Metal = Lithium, Sodium, Potassium) Batteries

Alkali-metal/sulfur batteries hold great promise for offering relatively high energy density compared to conventional lithium-ion batteries. By providing viable sulfur composites that can be effectively used, carbonaceous hosts as a key component play critical roles in overcoming the preliminary challenges associated with the insulating sulfur and its relatively soluble polysulfides. Herein, a comprehensive overview and recent progress on carbonaceous hosts for advanced next-generation alkali-metal/sulfur batteries are presented. In order to encapsulate the highly active sulfur mass and fully limit polysulfide dissolution, strategies for tailoring the design and synthesis of carbonaceous hosts are summarized in this work. The sticking points that remain for sulfur cathodes in current alkali-metal/sulfur systems and the future remedies that can be provided by carbonaceous hosts are also indicated, which can lead to long cycling lifetimes and highly reversible capacities under repeated sulfur reduction reactions in alkali-metal/sulfur during cycling.

Pathways of Developing High-Energy-Density Flexible Lithium Batteries

Flexible lithium-based batteries (FLBs) enable the seamless implementation of power supply to flexible and wearable electronics. They not only enhance the energy capacity by fully utilizing the available space but also revolutionize the form factors of future device design. To date, how to simultaneously acquire high energy density and excellent mechanical flexibility is the major challenge of FLBs. Here, a critical discussion for guiding the future development of FLBs toward high energy density and high flexibility is presented. First, the industrial criteria of FLBs for several desirable applications of flexible and wearable electronics are summarized. Then, strategies to achieve flexibility of FLBs are discussed, with highlights of representative examples. The performance of FLBs is benchmarked with a flexible battery plot. New materials and cell design principles are analyzed to realize high-energy-density and high-flexibility FLBs. Other important aspects of FLBs including materials to improve the cycling stability and safety are also discussed.

Electrocatalytic NiCo2O4 Nanofiber Arrays on Carbon Cloth for Flexible and High-Loading Lithium-Sulfur Batteries

Lithium-sulfur batteries have ultrahigh theoretical energy densities, which makes them one of the most promising next-generation energy storage systems. However, it is still difficult to achieve large-scale commercialization because of the severe lithium polysulfide (LiPS) shuttle effect and low sulfur loading. Here, we report a flexible lithium-sulfur battery of a high sulfur loading with the assistance of NiCo₂O₄ nanofiber array grown carbon cloth. The NiCo₂O₄ nanofibers are ideal electrocatalysts for accelerating LiPS conversion kinetics through strong chemical interactions. Therefore, the composite cathode delivers a high specific capacity of 1280 mAh g^-1 at 0.2 C with a sulfur loading of 3.5 mg cm^-2, and it can maintain a high specific capacity of 660 mAh g^-1 after 200 cycles, showing a good cycle stability. The "layer-by-layer" stacking strategy enables the Li-S battery with a high S loading of ∼9.0 mg cm^-2 to deliver a high areal capacity of 8.9 mAh cm^-2.

Fe-cation Doping in NiSe2 as an Effective Method of Electronic Structure Modulation towards High-Performance Lithium-Sulfur Batteries

The commercialization of Li-S batteries is hindered by the shuttling of lithium polysulfides (LiPSs), the sluggish sulfur redox kinetics as well as the low sulfur utilization during charge/discharge processes. Herein, a free-standing cathode material was developed, based on Fe-doped NiSe₂ nanosheets grown on activated carbon cloth substrates (Fe-NiSe₂ /ACC) for high-performance Li-S batteries. Fe-doping in NiSe₂ plays a key role in the electronic structure modulation of NiSe₂ , enabling improved charge transfer with the adsorbed LiPSs molecules, stronger interactions with the active sulfur species and higher electrical conductivity. Effective promotion of the sulfur redox kinetics and enhanced sulfur utilization were achieved under high areal sulfur loadings. The stronger interactions with LiPSs together with the unique 3D structure of Fe-NiSe₂ /ACC also induced the transformation of Li₂ S₂ /Li₂ S growth from conventional 2D films to 3D particles, significantly eliminating the barriers of solid nucleation and growth during the phase transition of liquid LiPSs to solid Li₂ S₂ /Li₂ S. With a high sulfur loading of 9.9 mg cm^-2 , the Fe-NiSe₂ /ACC cathode enabled a high area capacity of 9.14 mAh cm^-2 with a low average decay of 0.11 % per cycle over 200 cycles at 0.1 C.

Rambutan peel derived porous carbons for lithium sulfur battery

Porous carbons were prepared from the biomass waste rambutan peels using hydrothermal carbonization followed by the KOH activation process. Rambutan peel derived porous carbons (RPC) with high surface area of 2104 m2 g−1 and large pore volume of 1.2 cm3 g−1 were obtained at KOH/carbon ratio of 4 and activation temperature of 900 °C. The as-obtained porous carbons were capable of encapsulating sulfur with a high loading of 68.2 wt% to form RPC/S composite cathode for lithium sulfur (Li–S) battery. High specific discharge capacities of about 1275 mAh g−1 were demonstrated by the RPC/S composites at 0.1 C. After 200 cycles at 0.1 C, a high specific capacity of 936 mAh g−1 was maintained, showing an excellent capacity retention of about 73%.

Tailoring 3D Carbon Foam using CNTs and MnO2 to Fabricate Stable Lithium/Dissolved Lithium Polysulfide Batteries

The lithium-sulfur (Li-S) battery is an ideal electrochemical energy storage system owing to the high theoretical energy density and acceptable cost of finance and the environment. However, some disadvantages, including low electrical conductivity, poor sulfur utilization, and rapid capacity fading, obstruct its practical application. In this work, 3D carbon foam from a melamine resin is synthesized via high-temperature calcination. Carbon nanotubes (CNTs) and MnO₂ are utilized to tailor the properties of the 3D cathode collector in the liquid Li₂S₆-containing Li-S battery without additional conductive agents, binders, and aluminum foil. Herein, the decorated MnO₂ on the carbon fiber foam prolongs the lifespan of the Li-S battery, and adding CNTs is beneficial to enhance the capacity and cyclic performance of the Li-S battery under high sulfur loading. The Li-S battery with a sulfur loading of 3 mg cm^-2 possesses a reversible capacity of 437.9 mA h g^-1 after 400 cycles at 0.1 C. The capacity could be maintained at 568 mA h g^-1 at 0.1 C after 80 cycles when the sulfur loading increases to 6 mg cm^-2.

Material design strategies to improve the performance of rechargeable magnesium-sulfur batteries

Beyond current lithium-ion technologies, magnesium-sulfur (Mg-S) batteries represent one of the most attractive battery chemistries that utilize low cost, sustainable, and high capacity materials. In addition to high gravimetric and volumetric energy densities, Mg-S batteries also enable safer operation due to the lower propensity for magnesium dendrite growth compared to lithium. However, the development of practical Mg-S batteries remains challenging. Major problems such as self-discharge, rapid capacity loss, magnesium anode passivation, and low sulfur cathode utilization still plague these batteries, necessitating advanced material design strategies for the cathode, anode, and electrolyte. This review critically appraises the latest research and design principles to address specific issues in state-of-the-art Mg-S batteries. In the process, we point out current limitations and open-ended questions, and propose future research directions for practical realization of Mg-S batteries and beyond.

An Ultra-Long-Life Flexible Lithium-Sulfur Battery with Lithium Cloth Anode and Polysulfone-Functionalized Separator

Flexible and high-performance batteries are urgently required for powering flexible/wearable electronics. Lithium-sulfur batteries with a very high energy density are a promising candidate for high-energy-density flexible power source. Here, we report flexible lithium-sulfur full cells consisting of ultrastable lithium cloth anodes, polysulfone-functionalized separators, and free-standing sulfur/graphene/boron nitride nanosheet cathodes. The carbon cloth decorated with lithiophilic three-dimensional MnO₂ nanosheets not only provides the lithium anodes with an excellent flexibility but also limits the growth of the lithium dendrites during cycling, as revealed by theoretical calculations. Commercial separators are functionalized with polysulfone (PSU) via a phase inversion strategy, resulting in an improved thermal stability and smaller pore size. Due to the synergistic effect of the PSU-functionalized separators and boron nitride-graphene interlayers, the shuttle of the polysulfides is significantly inhibited. Because of successful control of the shuttle effect and dendrite formation, the flexible lithium-sulfur full cells exhibit excellent mechanical flexibility and outstanding electrochemical performance, which shows a superlong lifetime of 800 cycles in the folded state and a high areal capacity of 5.13 mAh cm^-2. We envision that the flexible strategy presented herein holds promise as a versatile and scalable platform for large-scale development of high-performance flexible batteries.

Preparation of a multifunctional P-CF@Mn3O4 composite as a structural anode material

The novel CF@Mn3O4 composite prepared in three steps displays considerable electrochemical characteristics and potential in the flexible vehicle.

In Situ Conversion of Metal-Organic Frameworks into VO2 -V3 S4 Heterocatalyst Embedded Layered Porous Carbon as an "All-in-One" Host for Lithium-Sulfur Batteries

Although lithium-sulfur batteries exhibit a fivefold higher energy density than commercial lithium-ion batteries, their volume expansion and insulating nature, and intrinsic polysulfide shuttle have hindered their practical application. An alternative sulfur host is necessary to realize porous, conductive, and polar functions; however, there is a tradeoff among these three critical factors in material design. Here, the authors report a layered porous carbon (LPC) with VO₂ /V₃ S₄ heterostructures using one-step carbonization-sulfidation of metal-organic framework templates as a sulfur host that meets all the criteria. In situ conversion of V-O ions into V₃ S₄ nuclei in the confined 2D space generated by dynamic formation of the LPC matrix creates {200}-facet-exposed V₃ S₄ nanosheets decorated with tiny VO₂ nanoparticles. The VO₂ /V₃ S₄  @ LPC composite facilitates high sulfur loading (70 wt%), superior energy density (1022 mA h g^-1 at 0.2 C, 100 cycles), and long-term cyclability (665 mA h g^-1 at 1 C, 1000 cycles). The enhanced Li-S chemistry is attributed to the synergistic heterocatalytic behavior of polar VO₂ and conductive V₃ S₄ in the soft porous LPC scaffold, which accelerates polysulfide adsorption, conversion, and charge-transfer ability simultaneously.

Electrochemical Insights, Developing Strategies, and Perspectives toward Advanced Potassium-Sulfur Batteries

The boosting demand for high-capacity energy storage systems requires innovative battery technologies with low-cost and sustainability. The advancement of potassium-sulfur (K-S) batteries have been triggered recently due to abundant resource and cost effectiveness. However, the functional performance of K-S batteries is fundamentally restricted by the vague understanding of K-S electrochemistry and the imperfect cell components or architectures, facing the issues of low cathode conductivity, intermediate shuttle loss, poor anode stability, electrode volume fluctuation, etc. Inspired by considerable research efforts on rechargeable metal-sulfur batteries, the holistic K-S system can be stabilized and promoted through various strategies on rational physical regulation and chemical engineering. In this review, first an attempt is made to address the electrochemical kinetic concept of K-S system on the basis of the emerging studies. Then, the classification of performance-improving strategies is thoroughly discussed in terms of specific battery component and prospective outlooks in materials optimization, structure innovations, as well as relevant electrochemistry are provided. Finally, the critical perspectives and challenges are discussed to demonstrate the forward-looking developmental directions of K-S batteries. This review not only endeavors to provide a deep understanding of the electrochemistry mechanism and rational designs for high-energy K-S batteries, but also encourages more efforts in their large-scale practical realization.

Enhanced Polysulfide Regulation via Porous Catalytic V2O3/V8C7 Heterostructures Derived from Metal-Organic Frameworks toward High-Performance Li-S Batteries

The development of Li-S batteries is largely impeded by the complicated shuttle effect of lithium polysulfides (LiPSs) and sluggish reaction kinetics. In addition, the low mass loading/utilization of sulfur is another key factor that makes Li-S batteries difficult to commercialize. Here, a porous catalytic V₂O₃/V₈C₇@carbon composite derived from MIL-47 (V) featuring heterostructures is reported to be an efficient polysulfide regulator in Li-S batteries, achieving a substantial increase in sulfur loading while still effectively suppressing the shuttle effect and enhancing kinetics. Systematic mechanism analyses suggest that the LiPSs strongly adsorbed on the V₂O₃ surface can be rapidly transferred to the V₈C₇ surface through the built-in interface for subsequent reversible conversion by an efficient catalytic effect, realizing enhanced regulation of LiPSs from capture to conversion. In addition, the porous structure provides sufficient sulfur storage space, enabling the heterostructures to exert full efficacy with a high sulfur loading. Thus, this S-V₂O₃/V₈C₇@carbon@graphene cathode exhibits prominent rate performance (587.6 mAh g^-1 at 5 C) and a long lifespan (1000 cycles, 0.017% decay per cycle). It can still deliver superior electrochemical performance even with a sulfur loading of 8.1 mg cm^-2. These heterostructures can be further applied in pouch cells and produce stable output at different folding angles (0-180°). More crucially, the cells could retain 4.3 mAh cm^-2 even after 150 cycles, which is higher than that of commercial lithium-ion batteries (LIBs). This strategy for solving the shuttle effect under high sulfur loading provides a promising solution for the further development of high-performance Li-S batteries.

Simple and Sustainable Preparation of Nonactivated Porous Carbon from Brewing Waste for High-Performance Lithium-Sulfur Batteries

The development of renewable energy sources requires the parallel development of sustainable energy storage systems because of its noncontinuous production. Even the most-used battery on the planet, the lithium-ion battery, is reaching its technological limit. In light of this, lithium-sulfur batteries have emerged as one of the most promising technologies to address this problem. The use of biomass to produce cathodes for these batteries addresses not only the aforementioned problem, but it also reduces the carbon footprint and gives added value to something normally considered waste. Here, the production, by simple and nonactivating pyrolysis, of a carbon material using the abundant "after-boiling waste" derived from beer brewing is reported. After adding a high sulfur loading (70 %) to this biowaste-derived carbon by the "melt diffusion" method, the sulfur-carbon composite is used as an effective cathode in Li-S batteries. The cathode shows excellent performance, reaching high capacity values with long-term cyclability at high current-847 mAh g^-1 at 1 C, 586 mAh g^-1 at 2 C, and even 498 mAh g^-1 at 5 C after 400 cycles-drastically reducing capacity loss to values approaching 0.01 % per cycle. This work demonstrates the possibility of obtaining low-cost, highly sustainable cathodic materials for the design of advanced energy storage systems.

A chemically stabilized sulfur cathode for lean electrolyte lithium sulfur batteries

Lithium sulfur batteries (LSBs) are promising next-generation rechargeable batteries due to the high gravimetric energy, low cost, abundance, nontoxicity, and high sustainability of sulfur. However, the dissolution of high-order polysulfide in electrolytes and low Coulombic efficiency of Li anode require excess electrolytes and Li metal, which significantly reduce the energy density of LSBs. Quasi-solid-state LSBs, where sulfur is encapsulated in the micropores of carbon matrix and sealed by solid electrolyte interphase, can operate under lean electrolyte conditions, but a low sulfur loading in carbon matrix (<40 wt %) and low sulfur unitization (<70%) still limit the energy density in a cell level. Here, we significantly increase the sulfur loading in carbon to 60 wt % and sulfur utilization to ∼87% by dispersing sulfur in an oxygen-rich dense carbon host at a molecular level through strong chemical interactions of C-S and O-S. In an all-fluorinated organic lean electrolyte, the C/S cathode experiences a solid-state lithiation/delithiation reaction after the formation of solid electrolyte interphase in the first deep lithiation, completely avoiding the shuttle reaction. The chemically stabilized C/S composite retains a high reversible capacity of 541 mAh⋅g^-1 (based on the total weight of the C/S composite) for 200 cycles under lean electrolyte conditions, corresponding to a high energy density of 974 Wh⋅kg^-1 The superior electrochemical performance of the chemical bonding-stabilized C/S composite renders it a promising cathode material for high-energy and long-cycle-life LSBs.

Recyclable Superhydrophobic, Antimoisture-Activated Carbon Pellets for Air and Water Purification

Activated carbon (AC) is a low-cost, highly porous material with large internal surface areas. It is highly efficient in absorbing moisture and a variety of chemical pollutants. Therefore, it has been widely used in air and water purification. However, the strong affinity to moisture often dominates, thus limiting AC's adsorption capacity of other pollutants in a humid environment and reducing its overall lifetime. In the study, superhydrophobic and anti-moisture AC (SA-AC) pellets are fabricated through one-step modification of commercially available AC with a solution consisting of superhydrophobic silica nanoparticles. The SA-AC pellets exhibit excellent water repellency with a static water contact angle reaching 160.3°. More importantly, they are moisture-resistant and air-permeable. Therefore, they preferably adsorb organic gases at humid conditions. The absorbed organic vapor can be released when they are transferred back to the dry atmosphere, for example, releasing approximately 35% of absorbed ethanol. The recoverability significantly reduces energy requirement compared to calcination or conventional extraction. Great adsorption capacity of organic dyes such as methylene blue, removal of oil-in-water microemulsions, and recyclability of SA-AC pellets are demonstrated. The morphology of the microporous structures of the SA-AC pellets is characterized against processing conditions, surface functional groups, and hierarchical structures tailored by the deposition of low-surface energy silica nanoparticles. The resulting micro-/sub-micropores on the pellet surface promote droplet condensation, thus displaying greater damp-proof performance than those treated by traditional modification. The study here presents a promising alternative for the efficient purification on large-scale air/water treatment.

Binder-Free Electrodes and Their Application for Li-Ion Batteries

Lithium-ion batteries (LIB) as energy supply and storage systems have been widely used in electronics, electric vehicles, and utility grids. However, there is an increasing demand to enhance the energy density of LIB. Therefore, the development of new electrode materials with high energy density becomes significant. Although many novel materials have been discovered, issues remain as (1) the weak interaction and interface problem between the binder and the active material (metal oxide, Si, Li, S, etc.), (2) large volume change, (3) low ion/electron conductivity, and (4) self-aggregation of active materials during charge and discharge processes. Currently, the binder-free electrode serves as a promising candidate to address the issues above. Firstly, the interface problem of the binder and active materials can be solved by fixing the active material directly to the conductive substrate. Secondly, the large volume expansion of active materials can be accommodated by the porosity of the binder-free electrode. Thirdly, the ion and electron conductivity can be enhanced by the close contact between the conductive substrate and the active material. Therefore, the binder-free electrode generally exhibits excellent electrochemical performances. The traditional manufacture process contains electrochemically inactive binders and conductive materials, which reduces the specific capacity and energy density of the active materials. When the binder and the conductive material are eliminated, the energy density of the battery can be largely improved. This review presents the preparation, application, and outlook of binder-free electrodes. First, different conductive substrates are introduced, which serve as carriers for the active materials. It is followed by the binder-free electrode fabrication method from the perspectives of chemistry, physics, and electricity. Subsequently, the application of the binder-free electrode in the field of the flexible battery is presented. Finally, the outlook in terms of these processing methods and the applications are provided.

Precipitated sulfur cathode—a hybrid faradaic and pseudocapacitive discharging process

A carbon-sulfur cathode was prepared by precipitating a suspension of acetylene black and dissolved sulfur from ethanol. The morphology of the cathode material was investigated using scanning and transmission electron microscopy. The diameter of commercial sulfur particles is between 20 and 50 μm, while this value for the precipitated sulfur was ca. order of magnitude lower (between 2 and 5 μm). Electrochemical properties of Li│S cells were investigated by cyclic voltammetry, galvanostatic discharging, and electrochemical impedance spectroscopy. Galvanostatic discharging curves of the Li│S system may be divided into three regions. At the beginning, the discharging undergoes at an approximately constant voltage (faradaic process) to switch into a pseudocapacitive process (two discharging regions characterized by linearly decreasing voltage). The hybrid discharging faradaic-pseudocapacitive nature implies the description of the total process by two types of capacities: in coulombs (faradaic process) and in farads (pseudocapacitive regions). The calculated experimental specific energy density (free enthalpy change) during the discharging process was ca. 1063 Wh kg−1, approximately twofold higher in comparison with such cathodes as LiFePO4 or LixMn2O4. These results show that the sulfur-carbon precipitated from ethanol can serve as a promising cathode for Li│S primary cells.

Straightforward synthesis of Sulfur/N,S-codoped carbon cathodes for Lithium-Sulfur batteries

An upgrade of the scalable fabrication of high-performance sulfur-carbon cathodes is essential for the widespread commercialization of this technology. Herein we present a simple, cost-effective and scalable approach for the fabrication of cathodes comprising sulfur and high-surface area, N,S-codoped carbons. The method involves the use of a sulfur salt, i.e. sodium thiosulfate, as activating agent, sulfur precursor and S-dopant, and polypyrrole as carbon precursor and N-dopant. In this way, the production of the porous host and the incorporation of sulfur are combined in the same procedure. The porous hosts thus produced have BET surface areas in excess of 2000 m² g⁻¹, a micro-mesoporous structure, as well as sulfur and nitrogen contents of 5–6 wt% and ~2 wt%, respectively. The elemental sulfur content in the composites can be precisely modulated in the range of 24 to ca. 90 wt% by controlling the amount of sodium thiosulfate used. Remarkably, these porous carbons are able to accommodate up to 80 wt% sulfur exclusively within their porosity. When analyzed in lithium-sulfur batteries, these sulfur-carbon composites show high specific capacities of 1100 mAh g⁻¹ at a low C-rate of 0.1 C and above 500 mAh g⁻¹ at a high rate of 2 C for sulfur contents in the range of 50–80 wt%. Remarkably, the composites with 51–65 wt% S can still provide above 400 mAh g⁻¹ at an ultra-fast rate of 4 C (where a charge and discharge cycle takes only ten minutes). The good rate capability and sulfur utilization was additionally assessed for cathodes with a high sulfur content (65–74%) and a high sulfur loading (>5 mg cm⁻²). In addition, cathodes of 4 mg cm⁻² successfully cycled for 260 cycles at 0.2 C showed only a low loss of 0.12%/cycle.

Flexible 3D carbon cloth as a high-performing electrode for energy storage and conversion

High-performance energy storage and conversion devices with high energy density, power density and long-term cycling life are of great importance in current consumer electronics, portable electronics and electric vehicles. Carbon materials have been widely investigated and utilized in various energy storage and conversion devices due to their excellent conductivity, mechanical and chemical stability, and low cost. Abundant excellent reviews have summarized the most recent progress and future outlooks for most of the current prime carbon materials used in energy storage and conversion devices, such as carbon nanotubes, fullerene, graphene, porous carbon and carbon fibers. However, the significance of three-dimensional (3D) commercial carbon cloth (CC), one of the key carbon materials with outstanding mechanical stability, high conductivity and flexibility, in the energy storage and conversion field, especially in wearable electronics and flexible devices, has not been systematically summarized yet. In this review article, we present a careful investigation of flexible CC in the energy storage and conversion field. We first give a general introduction to the common properties of CC and the roles it has played in energy storage and conversion systems. Then, we meticulously investigate the crucial role of CC in typical electrochemical energy storage systems, including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries and supercapacitors. Following a description of the wide application potential of CC in electrocatalytic hydrogen evolution, oxygen evolution/reduction, full-water splitting, etc., we will give a brief introduction to the application of CC in the areas of photocatalytically and photoelectrochemically induced solar energy conversion and storage. The review will end with a brief summary of the typical superiorities that CC has in current energy conversion and storage systems, as well as providing some perspectives and outlooks on its future applications in the field. Our main interest will be focused on CC-based flexible devices due to the inherent superiority of CC and the increasing demand for flexible and wearable electronics.